1. Field of the Invention
The present invention relates generally to transmission of broadcast television signals using high power amplifiers, and more particularly to improved oil-cooling of inductive output tube amplifiers which utilize a multiple segmented, depressed collector.
2. Background and Related Art
It is generally known in the art to use linear beam devices, such as klystrons or traveling wave tube amplifiers, to generate or amplify a high frequency RF signal. Such devices generally include an electron emitting cathode and an anode that has a central aperture. The cathode and anode are spaced apart, and an application of a high voltage potential between the two elements draws electrons from the cathode surface to form a high power electron beam that passes through the anode aperture.
One class of known linear beam device, known as inductive output tubes [xe2x80x9cIOTxe2x80x9d], further includes a grid positioned between the cathode and anode. An application of a RF signal to the grid relative to the cathode modulates the density of the electron beam. As the modulated electron beam propagates across a gap provided downstream within the IOT, RF fields are induced into a cavity coupled to the gap. The RF fields may then be extracted from the cavity in the form of a high power, modulated RF signal. The benefits of IOTs as power amplifiers in television transmitters, especially in common amplification configurations, are well known in terms of increased efficiency and reliability.
The performance of an IOT may be further improved through the use of a multistage depressed collector [xe2x80x9cMSDCxe2x80x9d]. The electrons of the modulated beam have widely varying energy levels as they exit from the output cavity. By using a multiplicity of collector electrodes which are depressed to potentials below that of the device body (i.e., the potential closer to the original electron beam energy), the spent electrons of the beam can be collected at the minimum possible energy. By recovering most of the remaining kinetic energy of the spent electron beam in depressed stages, higher operating efficiency can be achieved because less of the beam energy not used by the RE conversion is lost by conversion of kinetic energy into heat. An IOT with an MSDC is described in U.S. Pat. No. 5,440,202 to H. Mathews et al. for ELECTRON BEAM DEVICE HAVING A DIRECT CURRENT FEED WITH SWITCHING STAGES THEREIN, the subject matter of which is incorporated in the entirety by reference herein.
Even in an IOT with an MSDC, much of the energy of the electron beam is converted to thermal energy, which heats the components of the IOT. More specifically, the collector is heated by the thermal energy from the electron beam. Thus, the IOT, and the collector in particular, must be capable of withstanding very high operating temperatures, so it is necessary to construct the components of IOT such as the collector from heat resilient materials. However, the localized heat accumulation in the collector may distort the electron beam and otherwise degrade the performance. Accordingly, it is desirable to cool the IOT collector to improve performance.
It is generally known to cool other types of radio-frequency [xe2x80x9cRFxe2x80x9d] amplifiers. For example, U.S. Pat. No. 5,010,304 by Mueller et al. for CRYOGENICALLY-COOLED RADIO-FREQUENCY POWER AMPLIFIERS provides an amplifier that positions components of the amplifier onto a heat sink having at least one surface in contact with a cryogenic fluid. In this system, thermal energy is transferred from the amplifier to the heat sink to the cryogenic fluid. Similarly, U.S. Pat. No. 5,655,373 by Ju for ANTENNA MAST-TOP MOUNTABLE THERMO-ELECTRICALLY COOLED AMPLIFIER ENCLOSURE SYSTEM discloses an RF amplifier having a fan to create an air flow to cool the elements of the amplifier and to dissipate the thermal energy away from the amplifier. It is also generally known to use oil fluid to cool and insulate components of the amplifier, as suggested by U.S. Pat. No. 5,189,434 by Bell for MULTI-MODE ANTENNA HAVING PLURAL RADIATORS COUPLED VIA HYBRID CIRCUIT MODULES and U.S. Pat. No. 4,689,803 by Johannesssen et al. for ANTENNA TUNING SYSTEM AND METHOD.
A generally known cooled-IOT system uses a flow of ambient air to dissipate the radiant thermal energy from the IOT. However, the air-cooled system has limited ability to cool the collector because of the limited heat capacity of gases. Furthermore, the air flows have varying pressure and velocity, which allow unequal cooling of IOT. The unequal cooling may lead to the formation of relatively hot spots, which may degrade the collector of the IOT. This can result in failure of the vacuum integrity of the IOT.
Alternatively, another generally known cooled-IOT system uses the circulation of a water-based fluid to remove the thermal energy from the IOT. However, water-based fluids are inherently incompatible with high-powered electrical applications, especially where there are voltages on the elements which need cooling. For example, the water-based fluid may damage the delicate electronic circuitry of the IOT. In addition, electrolysis may occur in a system containing a water-based fluid. As a result, the water-cooled systems are relatively expensive to produce because it requires use of high grade plastics and stainless-steel based pumps for proper operation of the system. Furthermore, the water-based fluid cooling systems are relatively expensive and difficult to maintain. The use of water-based fluid as a cooling media requires careful engineering to prevent the water-based fluid from damaging the electronic circuitry and to prevent electrolysis from occurring in the system. In particular, the water-based fluid must be continually purified to remove contaminants that will contribute to electrolysis that will damage the IOT. The water-cooled system also requires periodic maintenance to maintain correct operation.
Thus, it is the goal of the present invention to provide a liquid-cooled IOT system that effectively cools the IOT and is relatively inexpensive to build and easy to maintain.
Accordingly, the present invention provides a solution to the shortcomings of the prior art as discussed above.
In particular, the present invention provides a system and corresponding method for an oil-cooled IOT. In one embodiment, the system comprises an IOT, a fluid passageway in thermal contact with the IOT, an oil-based fluid within the fluid passageway such that the oil-based fluid removes thermal energy from the IOT, a fluid pump connected to the fluid passageway to circulate the oil-based fluid, and a fluid heat-exchanger connected to the fluid passageway for removing the thermal energy from the oil-based fluid. The IOT preferably has an MSDC, and the oil-based fluid is preferably commercially available transformer oil.
In a preferred embodiment of the present invention, the oil-heat exchanger is connected to an external heat exchanging system. The external heat exchanger has a cooling fluid passageway in thermal contact with the oil-fluid passageway. Within the cooling fluid passageway is a cooling fluid that absorbs the thermal energy from the oil-based fluid. Also connected to the cooling fluid passageway is a cooling fluid pump that circulates the cooling fluid and an external cooling fluid heat exchanger that removes the thermal energy from the cooling fluid. This cooling fluid can be a water-based fluid or air.